1. Field of the Invention:
This invention relates to a head moving apparatus for moving a magnetic head or the like for writing or reading a signal in or out of a floppy disk to a desired position and, more particularly, to a head moving apparatus using a stepping motor.
2. Description of the Prior Art:
The stepping motor usually has a hysteresis characteristic, due to which it is stopped at a deviated position after the completion of driving if there has been a load on its output shaft. More specifically, the stepping motor has an output torque characteristic as shown in FIG. 1. Under an ideal load-free condition, the rotor can be driven to and stopped at a position .theta..sub.0, at which the generated torque is zero either in the forward or reverse direction with a step angle .theta..sub.s in a range of +.theta..sub.s and -.theta..sub.s. However, if there is a load applied to the rotor, i.e., output shaft thereof, the rotor cannot be driven in an output torque range +.theta..sub.L to -.theta..sub.L below the load torque T. Therefore, the rotor is stopped, and the stop position of the rotor is determined in the afore-mentioned range of +.theta..sub.L to -.theta..sub.L due to momentum of the rotor including the load. Therefore, the rotor is stopped at different positions depending on whether the stepping motor is driven forwardly or reversely.
For example, when the head is moved from a position of a (N+1)-th address to a position of a N-th address as shown in FIG. 4, it is stopped at position a, whereas when it is moved from a position of a (N-1)-th address to a position of the N-th address, it is stopped at a position b.
In the usual floppy disk apparatus, there are cases when the magnetic head is moved to a desired track position on the floppy disk from the side of the center of the disk toward the outer periphery thereof and also from the side of the outer periphery of the disk toward the center thereof. Therefore, a head moving apparatus is necessary, which can move the magnetic head in either direction.
The head moving apparatus is required to accurately stop the magnetic head at a desired track position on the disk when the head is moved in either direction.
In case of a head moving apparatus, in which the head is moved using a stepping motor, however, it is difficult to accurately stop the head at a desired position due to the hysteresis characteristic of the stepping motor as noted above. Particularly, where this head moving apparatus is employed in a floppy disk apparatus which is arranged to reduce the track pitch so as to increase the recording density, it is impractical unless errors in the stop position of the head due to the hysteresis characteristic are reduced.